With the term “reciprocal position between the cylinder and piston” in the current description and in the following claims it means the distance traveled by a piston, during its motion in the respective cylinder, respect to an own stand-off position. For example, in case of a cylinder-piston unit having double effect, the stand-off position of a piston coincide to the position in which it stands at the same distance respect to both the head's extremities of the respective cylinder.
In the state of the art in order to know continuously the reciprocal position between a cylinder and its respective piston in it translatable, it expects to obtain a reference codification, located on the rod of the piston, for example manufactured with stainless steel. Such reference codification is obtained for example with laser marking technology, in a predefined length' section of the piston's rod and it usually shows both marked zones and unmarked zones. Such sections of the reference codification, marked or unmarked, reflect in different way the light radiations on them incident.
A portion of reference codification is detectable continuously, during the piston's motion in the cylinder, through suitable detecting means which are usually arranged in the cylinder of the cylinder-piston unit. The portion of reference codification detectable continuously from the detecting means is correlatable to the reciprocal position between cylinder and piston.
The traditional detecting means include an emitter means of light radiations, destined to hit, in use, a section of the piston's rod surface and a respective sensor's means, in charge to detect such light radiations reflected from the rod's surface and to emit, in output, an suitable output signal.
As disclosed above, the survey of a section of reference codification, on the piston's rod, is based on the reflection's difference of the light radiations, incident on the rod itself. The light radiations produced from the emitter means are, indeed, reflected almost totally from the unmarked surface of the piston's rod, while they are indeed in majority absorbed, when they are incident on a marked surface of the rod. The consequence is that the electrical signal at the output of the sensor's means, typically analogue type, presents, in correspondence to a code' section of processed code (marking), a different amplitude in comparison to the one detectable in correspondence to a section of rod which is not interested to such process.
The output signal of the sensor's means is expect to be later continuously elaborated from a control and elaboration data unit, that, emits at the output an index correlated to the reciprocal position in that moment acquired between cylinder and piston.
A typical example of reference codification achievable on a rod of a piston is taught in U.S. Pat. No. 6,327,791. In such document the reference codification includes a bar code obtained along the rod of the piston for a section of defined length, which bar code represents a binary codification two or more bit long. Progressively the piston travels in the respective cylinder, the detectable codification section, in use, from the detection means, in correspondence to one detection's zone of theirs for this purpose considered, changes, thus originating a binary code from time to time different. Each detectable binary code in correspondence of the detecting zone is correlatable to a specific position between cylinder and piston and therefore, based of the reading of a section of reference codification, it is possible to obtain the reciprocal position in that moment represented/acquired between cylinder and piston.